video: adf: add helpers for validating custom formats

Many custom formats look a lot like the standard ones, but with
different subsampling, bpp, etc.  Expose and document
adf_buffer_validate()'s main body, so drivers can reuse its logic when
validating these formats.

Change-Id: I1d06981c9e5aab26f3ab2956c08c679f2c823bcc
Signed-off-by: Greg Hackmann <ghackmann@google.com>
video: adf: make dpms_state sysfs attribute writable

Change-Id: I04e7785cbddac160003e6c9edaf62d20b367fdc9
Signed-off-by: Greg Hackmann <ghackmann@google.com>
video: adf: set default interface dpms_state to OFF

Interfaces default to unplugged, so they should also default to off

Change-Id: I36500a54b11f354a0d7dd2c9924a79e0d9c6f855
Signed-off-by: Greg Hackmann <ghackmann@google.com>
video: adf: expose adf_modeinfo_set_{name,vrefresh} to drivers

Change-Id: Id9f8b2184927a77b244ce0b33d619d6e44a0f17a
Signed-off-by: Greg Hackmann <ghackmann@google.com>